The production graph is based on the annual reports of the Netherlands Cancer institute (NKI). In these reports the total number of irradiation sessions with radium or X-ray treatment are given for each year. The number of irradiated patients is not explicitly shown in the annual reports. The ratio between the number of patients receiving radium and X-ray treatments can be estimated by interpreting the number of sessions as follows.
For X-ray treatments a large number of fields were irradiated. It is assumed that a total of 30 sessions is not unusual for a X-ray treatment. A radium treatment however, was carried out in a small number of sessions, presumably 1 to 2. Just to give an idea of the ratio between the number of patients treated with X-rays and those treated with radium, the production figures for radium treatments are multiplied by 15.
The graph shows that radium or X-ray treatments are varyingly preferred. An impression of the background of developments can be obtained from the various reports. The growing number of patients puts pressure on the clinic. During the pioneer phase 1915 - 1920, the use of X-rays, initially in combination with radium, increases rapidly. Complex irradiation techniques with X-ray beams are developed. From 1919, this is even more so due to the harder radiation of 200 kV becoming available. In the 1920's, after bad experience with the primitive dosimetry and localisation of the X-ray beam, radium treatments are given more often. Around 1928 after the introduction of accurate dosimetry, with introduction of the dose unit "röntgen" and the ionisation chambers, the use of X-ray irradiation increases strongly again while the use of radium gradually decreases. Also, improved X-ray machines come into use and the available voltage increases up to 250 kV.